There are various methods that can be used for snipers detection and locating weapon fire, including small arms. The phenomena utilized by these methods include the so-called muzzle blast and flash; the shock wave, vortex, and thermal signature of the bullet in flight; and retro-reflection from the sniper's optical sight. Other phenomena, for instance disturbances of the refractive index of atmosphere caused by vortices shed by the bullet in flight, can potentially be utilized for snipers detection.
One of the optical signals caused by weapon firing is the muzzle flash, which is the incandescent flash at the weapons muzzle caused by the ignition of oxygen, the expulsion of burning powder grains and the expansion of powder gasses. The phenomenon of muzzle flash is more clearly pronounced in various assault rifles, short barrel infantry weapons, and “cut down” weapons. For instance, in a short barrel, the bullet can leave the barrel before the powder is completely burnt. In this case, the unburnt powder ignites in the air, giving off a bright flash. For a shooter, muzzle flash presents a serious problem: it increases the shooter visibility to the enemy and obscures the target view. As a result, the shooter using a weapon generating muzzle flash must move quickly after firing to avoid return fire.
Although muzzle flash can be partially hidden by flash suppressors or partially reduced by using cartridges with a faster-burning gunpowder, so that the propellant gases will already have begun to cool by the time they exit the barrel, this is not always convenient for the shooter. For example, the size of a device necessary to hide the muzzle flash from an enemy can be too large.
For the side opposite to a shooter, a problem consists in a muzzle flash detection, which can be considered as one of high speed imaging applications. For purposes of study, such detection can be done in the laboratory.
At the present time, a few muzzle flash detecting systems can be used in the battle field. Examples of such systems include Radiance Technologies' WeaponWatch™, RAFAEL's SPOTLITE, Maryland Advanced Development Lab's VIPER. The VIPER equipment, for example, consists of a mid-wave infrared (MWIR) camera, together with real-time signal processing, magnetic compass, and user display and alarm. It is advertised as providing gun detection within 70 msec after gunfire and geolocation of the firing event. Using MWIR-camera also allows concurrently performing forward looking infrared imaging (FLIR) of a region of interest.
The known snipers detection methods also suffer from various problems. One of the problems associated with MWIR cameras, is that these cameras are expensive and bulky. Most of them are based on cryogenically cooled fast refresh-rate detectors.
Uncooled infrared sensors for an Integrated sniper location system were studied in [8]. The system of [8] had a focal plan array size of 320×240 pixels allowing a field of view of 20 (H)×15 (V) degrees with an accuracy of 2 mrad. The system's weight was 5 pounds, frame rate 60 Hz, size 12.2 (L)×5.0 (W)×4.1 (H) inches, noise equivalent input 5.6×10-12 W/cm2, and power consumption 9V. The projected price of the device was about $10,000. The uncooled bolometric detectors are typically significantly slower than the muzzle flash, and thus the signal is smeared over a long time harming the signal to noise ratio (SNR). These detectors are mostly sensitive to the 8-12 um range, where the signature is relatively low.
Other countersniper systems, such as relying on acoustic signals (e.g. muzzle blast and bullet shock wave), may be lighter and lower in cost than systems based on cooled detectors. However, the acoustic countersniper systems typically have low angular accuracy and performance which is reduced in urban terrain, due to sound reflections.
Also, detection of rifle, sniper and small arm shooting or firing can be in principle done by the solar blind UV (SBUV) imaging technology and used for force protection and snipers detection. The UV signature of the firing is due to the secondary burning of the residual gun powder, ejected from the barrel. Nevertheless, this signature is also relatively small and may not provide usable detection range and acceptable false alarm rate. Some design and manufacturing of SBUV imaging systems is done, for example, by Ofil LTD (http://www.sbuv.com).
In principle, various detection methods can be combined with each other. Also, a muzzle flash detected by any method can be shown on a scenery image obtained by imaging with visible light. For example, technology of the Ofil LTD utilizes a bi-spectral visible-UV DayCor® camera and is aimed and presenting such combined images.